Thread grinding wheel



947. x J. E. WAlNWRlGHT 2,426,290

THREAD GRINDING WHEEL Filed July 2, 1945 Patented Aug. 26, 1947 2,426,290 THREAD GRINDING WHEEL John Ernest Wainwright, Coventry, England, as-

signor to Coventry Gauge & Tool Company Limited, Coventry, England Application July 2, 1945, Serial No. 602,778

. In Great Britain July 20,.1944

9 Claims.

In the production of screw threads of fine pitch by means of a multi-ribbed grinding wheel it. is necessary owing to the difiiculty or impossibility of forming or dressing the Wheel, to use a factored wheel, that is to say, a multi-ribbed wheel in which the pitch of the ribs .or serrations is a multiple of the pitch of the required screw thread.

The disadvantage of using a wheel of this kind is that the weakest parts of the serrations, viz: the crest portions are subject to the greatest wear.

An object of the present invention is to obtain a more uniform distribution of wear on the wheel.

A further object of the invention is to enable a dressing tool of a more robust form to be employed than is at present practicable, and at the same time to allow for the development of wear of the tool. l

With these and other objects in view the, inven tion consists in producing. a multi-ribbed grinde ing wheel in which the effective flanks function as those of a factored wheel butin which the pitch of the crests is equal to the pitchoi the required screw thread. l

In the method which is adopted according to this invention in forming a multi-ribbed grinding wheel having the above and other characteristics, a dressing tool moving across the peripheral face of the wheel, is given a depth component motion such as to form certain of the ribs at half the included angle of the required screw thread and the other ribs at an angle less than half the included angle of the thread. The effect of the dressing operation is to produce a modified form of factored wheel, the modification consisting, in effect, in the formation between each pairoi ade jacent ribs having a pitch which is a multiple of that of the required screw thread, of one or more intermediate or auxiliary ribs the flanks or" which are formed at such an angle to the axis of the wheel as to permit of the use of a dressing tool of a more robust form than could otherwise be employed, and to allow for wear of said tool.

In the accompanying drawing,

Figure 1 represents in longitudinal section a portion of the periphery of a multi-ribbed grinding wheel embodying one iormof the present invention, and a portion of a screw thread produced thereby.

Figure 2 is a similar View in which the crest portions of the sharper or more acuteangled ribs 2 a are formed to; the normal angle of the required thread.

Figure 3 is another similar view of a development of that shown in Figure 1.

In the drawing, a represents the multi-ribbed periphery of the improved grinding wheel and b a portion of the Work-piece, both of which are drawnto a very large scale.

As will be seen, the ribs 0 of the wheel are of normal form and have a pitch which is a multiple of that of the screw thread on the work-piece b. The ribs rd, however, which alternate with the ribs 0 have their flanks inclined at a greater angleto the axis of the wheel. The crests of the ribs d may either be left sharp and somewhat higher than those of the ribs 0, as shown in Fig- Iures 1 and 3, or may be formed at the normal angle and height, as seen in Figure 2, according to'the nature of the work to be screw-threaded. For certain purposes, as in the case of screw threaded gauges it is desirable to leave a clearance at thebottom of the thread, as shown at e in Figure 1, and more particularly in Figure 3. This is known as parting out, the depth of which can be varied as desired.

The flanks of the ribs 0 and d, referred to herein and in the claims, are the relatively inclined axially presented surfaces of said ribs, while the crests are the radial extremities or edges defined by the intersections of the respective flanks of said ribs 0 and d.

In dressing a wheel for producing, say, a V thread the depth component motion of a dressing tool moving across the face of the wheel, is completed in four successive strokes commencing, say, at the periphery of the wheel, as follows:

1. Entering the wheel at 60 to wheel axis and after forming one flank complete, carrying the tool further in the same direction a pre-deter- "mined amount.

the flank angle of the ribs (1 and the depth of cut.

Where it is desired to form the crests of the ribs at the normal angle, as shown in Figure 2,

the motion of the tool between forming the 70 flanks may revert to normal.

These motions of the dressing tool, which may be varied in order and magnitude, may be imparted by any desired means, such as by means of an appropriately formed cam, or by pantograph mechanism from an enlarged master or former.

By means of this invention not only is the dressing operation greatly facilitated but the wheel will retain its form for longer periods of continuous use than hitherto and hence its productive capacity will be proportionately increased.

A further advantage of the improved method of dressing herein described is that the production of the different parts of the form is independent of wear on the tool so that a composite self-contained form can be produced which is clearly defined at the junction of its several parts.

I claim:

1. A multi-ribbed grinding wheel for producing screw threads in which the flanks of certain of the ribs are inclined to the rotational axis of the wheel at the normal flank angle of the required screw thread and in which the flanks of the other ribs are inclined to said axis at an angle greater than said normal.

2. A multi-ribbed grinding wheel for producing screw threads in which ribs having their flanks inclined to the axis of the wheel at the same angle as the thread to be produced alternate with ribs having their flanks inclined to said axis at an angle less than the angle of said thread.

3. A multi-ribbed grinding wheel for producing screw threads comprising, a plurality of thread crest grinding ribs formed around the periphery of the grinding wheel and relatively axially spaced from each other by distances equal to a multiple of the pitch of the threads to be formed by said grinding wheel, the cross-sectional shape and dimensions of the base portions of said ribs corresponding to the cross sectional shape and dimensions of the radially outer portions of the grooves between the threads to be formed by said Wheel, in combination with a plurality of thread base grinding ribs disposed between said crest grinding ribs and of at least the same diameter as said crest grinding ribs, the cross-sectional shape and dimensions of the radial extremities of said base grinding ribs corresponding to the crosssectional shape and dimensions of the bottoms of the grooves between the threads formed by the grinding wheel, said base grinding ribs being of smaller axial dimensions at their base portions than said crest grinding ribs and thus engaging the work piece only at their radial extremities, such arrangement facilitating the dressing of the grinding wheel and serving to distribute the wear thereon so as to permit a, greater amount of use thereof between dressings.

4. A multi-ribbed grinding wheel for producing screw threads comprising, a plurality of thread crest grinding ribs formed around the periphery of the grinding wheel and relatively axially spaced from each other by distances equal to a multiple of the pitch of the threads to be formed by said grinding wheel, the base portions of said ribs being of suitable configuration and dimensions to grind the radially outer portions of the threads to be formed by said wheel, in combination with a plurality of thread base grinding ribs respectively disposed between said crest grinding ribs and of at least as great diameter as said crest grinding ribs, the radial extremities of said base grinding ribs being of suitable configuration to grind the bases of the threads to the desired shape, said base grinding ribs having smaller axial dimensions at their radially inner portions than said crest grinding ribs and thus engaging the work piece only at their radial extremities.

5. A multi-ribbed grinding wheel for producing screw threads comprising, a plurality of thread crest grinding ribs formed around the periphery of the grinding wheel, the radially inner portions of said ribs being of suitable configuration and dimensions to grind the crests of the threads formed by said wheel, in combination with a plurality of thread base grinding ribs respectively disposed between said crest grinding ribs and of at least as great diameter as said crest grinding ribs, the radial extremities of said base grinding ribs being of suitable configuration and dimensions to grind the bases of the threads formed by said wheel to the desired shape, said base grinding ribs having smaller axial dimensions than said crest grinding ribs.

6. A multi-ribbed grinding wheel for producing screw threads comprising, a plurality of thread crest grinding ribs formed around the periphery of the grinding wheel, the radially inner portions of said ribs being of suitable configuration and dimensions to grind the crests of the threads formed by said wheel to the desired shape, in combination with a plurality of thread base grinding ribs respectively disposed between said crest grinding ribs and or greater diameter than said crest grinding ribs, the radial extremities of said base grinding ribs being of suitable configuration and dimensions to grind the bases of the threads formed by said wheel to the desired shape, said base grinding ribs being of smaller maximum axial dimensions than said crest grinding ribs.

7. A multi-ribbed grinding wheel for producing screw threads comprising, a thread crest grinding rib extending around the periphery of the grinding wheel, the radially inner portion of said rib being of suitable configuration and dimensions to grind the crests of the threads formed by said wheel to the desired shape, in combination with a thread base grinding rib of at least as great diameter as said crestgrinding rib extending around the periphery of the grinding wheel adjacent said crest grinding rib, the radial extremity of said base grinding rib being of suitable configuration and dimensions to grind the bases of the threads formed by said wheel to the desired shape, said base grinding rib being of smaller maximum axial dimension than said crest grinding rib and thereby facilitating insertion and operation of a dressing tool between said ribs.

8. A multi-ribbed grinding wheel for producing screw threads comprising, a thread crest grinding rib extending around the periphery of the grinding wheel, the radially inner portion of said rib being of suitable configuration and dimensions to grind the crests of the threads formed by said wheel to the desired shape, in combination with a thread base grinding rib of greater diameter and smaller maximum axial dimension than said crest grinding rib extending around the periphery of the grinding wheel closely adjacent said crest grinding rib, the radial extremity of said base grinding rib being of suitable configuration and dimensions to grind the bases of the threads formed by said wheel to the desired shape. 7

9. A multi-ribbed grinding wheel for producing screw threads in which the flanks of certain of the ribs thereof are inclined to the axis of the 5 wheel at the normal flank angle of the required screw thread and in which these flanks extend radially from the wheel to an amount greater than the depth of the normal thread and in which the flanks of the other ribs are inclined 5 to said axis at an angle greater than said normal and which extend radially the same amount from the wheel as the flanks on said first-mentioned ribs.

JOHN ERNEST WAINWRIGHT.

REFERENCES CITED The following references are of record in the file of this patent:

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